Balloon catheters are used in the treatment of a variety of medical conditions. They are used extensively in conjunction with urinary, biliary, and vascular procedures. Among the more frequent uses for balloon catheters, however, is in vascular angioplasty of the peripheral and coronary arteries.
A vascular angioplasty procedure dilates the arteries that are obstructed (the stenosis), thereby improving blood flow through that region of the vasculature. In a typical angioplasty procedure, a balloon catheter is inserted percutaneously into the patient's arterial system. This percutaneous insertion is usually through the femoral artery. Once inside the patient's arterial system, the balloon catheter is advanced until the distal end of the catheter, where the balloon resides, is disposed adjacent to the obstruction. Once adjacent the stenosis, the balloon is inflated under fluid pressure to dilate the artery in the region of the stenosis.
Stents and stent delivery assemblies are utilized in conjunction with vascular angioplasty. Because dilated stenoses are known to reobstruct, a stent is often implanted to maintain the patency of the vessel.
A stent is a generally cylindrical prosthesis which is introduced, via a balloon catheter, into a lumen of a body vessel. The stent is positioned, and secured onto, the balloon in a configuration having a generally reduced diameter. Once the balloon catheter is positioned adjacent the desired location within the vasculature, the balloon is expanded. This balloon expansion subsequently causes the stent to increase its radial configuration from a reduced diameter (delivery diameter) to an expanded one (deployment diameter). In its expanded configuration, the stent supports and reinforces the vessel wall while maintaining the vessel in an open and unobstructed configuration.
The structure and finctions of stents are well known. Stents used in conjunction with vascular angioplasty are shown in U.S. Pat. No. 5,064,435 to Porter; U.S. Pat. No. 5,071,407 to Tenmin et al.; U.S. Pat. No. 5,221,261 to Termin et al.; U.S. Pat. No. 5,234,457 to Anderson; U.S. Pat. No. 370,691 to Samson; U.S. Pat. No. 5,378,239 to Termin et al.; U.S. Pat. No. 5,401,257 to Chevalier, Jr. et al.; and U.S. Pat. No. 5,464,450 to Buschemi et al., all of which disclosures are incorporated herein by reference.
A distinguishable feature between stents is whether they are self-expanding or balloon expandable. Both self-expanding and balloon expandable stent are well known and widely available. The present invention is particularly concerned with enhanced stent securement and safer stent loading in the delivery and deployment of balloon expandable stents.
Balloon expandable stents are crimped to their reduced diameter about the balloon portion of the catheter assembly. The stents are gently crimped onto the balloon either by hand, or with a tool. Once the stent is mounted, the catheter system is ready for delivery. There are, however, two complications associated with crimping stents to balloon atheters: (1) excessive crimping may damage the stent, the balloon, or the inner lumen of the catheter; and (2) inadequate securement force results in failure of the stent to maintain its axial position during advancement within the human anatomy.
Most expandable stents have an minimum compression diameter. The minimum compression diameter is the smallest radial profile that a stent may be reduced to without causing damage to the stent. This damage often decreases the functionality and reliability of the stent's expansion, as well as its ability to maintain the patency of a vessel wall. Furthermore, the stent must be crimped over that portion of the balloon which is expandable in order to have the entire length of the stent expanded against the vessel wall on deployment. The expandable portion of present balloons typically have an insufficient outer diameter for direct attachment of a stent in the balloon's folded, deflated configuration. Therefore, crimping a stent on this section alone will cause the stent to bend undesirably or it will not be held adequately in axial position without artificially building-up the diameter under the balloon --or other means to create bulk for stent crimping.
Maintaining the stent's axial position during the advancement of the catheter to the deployment site is critical. If a stent is not adequately compressed upon the balloon, the stent may fail to secure properly to the catheter assembly and could be dislodged from the catheter during advancement within the human anatomy. It is important, therefore, that the location where the stent is to be secured have an outer diameter (in the folded deflated configuration) greater than or equal to the stent's minimum compression diameter so that it may be firmly secured to the balloon catheter assembly. There are a number of devices used for maintaining a stent's axial securement about the balloon catheter.
U.S. Pat. No. 4,950,227 to Savin et al., relates to a stent delivery system in hich a sleeve overlaps the distal or proximal margin (or both) of the stent during delivery. This sleeve maintains the stent's axial position during the advancement of the catheter assembly to the deployment site. To deploy the stent, the stent margins are freed of the protective sleeve(s) and the sleeve then collapses toward the delivery catheter for removal.
PCT International Application No. WO 98/07390, published Feb. 26, 1998, discloses a delivery catheter using mounting bodies that have outer diameters exceeding the minimum compression diameter of a stent. The outer diameters of the mounting bodies are also circumferentially larger than the deflated balloon diameter. Therefore, the stent is crimped securely upon the mounting bodies in order to insure axial position during the catheter's advancement. The use of mounting bodies, however, affects the flexibility of the inner shaft within the balloon which is not desired. This application is incorporated herein by reference.